Has anyone measured the ACTUAL compression ratio?

[garth285]

Just like the title states has anyone actually measured the combustion chamber and piston, etc. of the 08-12 250r to find out the actual compression ratio?

[Racer x]

No
For me it changed from stock after the head is polished.
To do it You need a cc measuring set up. And a third grader with a calculator to do the math. A Thread on how would be great. I would be interested to see what they are.

[garth285]

I've done it on some other bikes before I just didnt want to tear into this engine :-/ but I do have a spare so yeah thats good.

Racer X I may have some up with a VERY cost effective way to lower our compression :-)

[kxpower?]

Sub'd

[Brother Michigan]

You should be able to measure the compression ratio with a simple compression gauge. You know what atmospheric pressure is to a pretty good degree, so screw in the gauge, measure the greatest pressure, and take a ratio of the two. Make sure to close your petcock or disconnect the injectors beforehand. Do it a few times and you can build up an idea of the uncertainties inherent in the gauge you're using.

[kxpower?]

Originally Posted by Brother Michigan

You should be able to measure the compression ratio with a simple compression gauge. You know what atmospheric pressure is to a pretty good degree, so screw in the gauge, measure the greatest pressure, and take a ratio of the two. Make sure to close your petcock or disconnect the injectors beforehand. Do it a few times and you can build up an idea of the uncertainties inherent in the gauge you're using.

It's not quite that simple but there's a way to measure the combustion chamber volume by measuring how much liquid the head + the piston dish volume or - the piston dome volume, plus volume added by the head gasket. From there it's just

CR=(displacement + CCV)/CCV


A lot of (auto) road racing bodies set a max compression ratio, they have this burette looking thing at the shop my brother co-ops in that they use to meter the water into the combustion chamber.

[Brother Michigan]

It's not perfect, but treating the air like an ideal gas and assuming isothermal compression (not really reasonable assumptions, but probably enough to get you to within a few percent), the ratio of compressed to uncompressed pressures does give the compression ratio.

[garth285]

Originally Posted by Brother Michigan

It's not perfect, but treating the air like an ideal gas and assuming isothermal compression (not really reasonable assumptions, but probably enough to get you to within a few percent), the ratio of compressed to uncompressed pressures does give the compression ratio.

That might be able to give you a ball park reading but I'm looking for 100% accurate measurements....

I just might have to do this myself but I've done it before its really not that bad although I forget how I measured the piston side....

Plexiglass with a hole in it, grease around the combustion chamber and a syringe with water.

I just looked online and they do the same thing with the piston but with the piston in the hole.

[alex.s]

on the 40cc bikes we put sillicone down the spark plug hole at tdc and then disassemble, remove and weigh it to calculate a volume, then you can do basic math for the rest of the cylinder

[garth285]

I sent out some eamils to JE and Wiesco hoping they would be willing to give me atleats the Piston Dome Volume but I doubt they would lol.

[garth285]

@Racer x Do you think 8.5 or 9.0 :1 ratios will be to low for these turds and the VZ21 turbo?

[Racer x]

I wish I could say. I am going to start with 12.5 to 1 and polish the piston tips to remove sharp edges and the same with the head. This should be 11.8-12 to 1. I don't know how much you need to spin the turbo. But I know if the engine has less than 125 psi compresson it will not start.

[garth285]

10-4 well I Wiesco got back to me and sent me this:

Hello Shawn,

Thanks for the inquiry. Our 40062M06200 is 12.5:1 CR, with a
+3.1cc dome. We do not offer a low compression piston for the Ninja
250, but we could look at custom building this for you. We would have
to place an order for a minimum of 12 pistons and rough pricing would be
$157ea, (rings, pin, and clips all included). If you are interested in
having parts built, please give me a call at 800-321-1364 x3109 and we
can go over more of the details.

[garth285]

OK @Racer x here is what I was thinking for lowering the compression.. Obviously we know we can get a set of custom pistons made which that will be a nice $1,900. We can also run a spacer under the cylinder as well a .080" spacer should lower it by about 1.5-2 points I believe but wed probably need adjustable cam gears.

How about this idea..... Ninja 300 rods? They are about 2.8mm shorter, I did some rough calculations and I think it might drop the compression to much, like down to 7-7.5:1... so if we ran the 300 rods with 12.5-13.0:1 pistons it might bring it up to the 8.5-9.0:1 ratio we'd be looking for without having to run block spacers and such?

Benefits - Newer (possibly stronger) rods, little thicker on the small end and youd get a forged piston with it.

Sorry all you N/A guys I'm trying to think of ideas for the turbo setup :-p

[garth285]

Know what else I just thought of, looking at the ninja 300 piston, they moved the pin location UP which means the piston would actually sit lower in the block.... HMMMMMM

[Racer x]

I would not do the 300 rods myself. I have Carillo rods and love them. And if you go with custom Pistons. I have a good friend ,John Noonan at Wossner that can make custom Pistons. And he knows land speed racing.
If you want to go with thicker gaskets. Thick copper is good. Head gaskets.com has the pattern already and I have the gaskets. Ask to speak to Mordy Dunst.

The cam timing would have to be adjusted for the taller head distance.

[jkv45]

Originally Posted by garth285

Do you think 8.5 or 9.0 :1 ratios will be to low for these turds and the VZ21 turbo?

That is generally regarded as close to optimum.

Here's some interesting reading on the subject - http://www.xcceleration.com/cr-boost%20101.htm

[Racer x]

My plan because I am running at high altitude is high compresson low boost. And that chart says 11 to one with 7.5 lb of boost is about 17 to 1 and that is what I want. And why j have Carillo rods

[kxpower?]

Originally Posted by garth285

OK @Racer x here is what I was thinking for lowering the compression.. Obviously we know we can get a set of custom pistons made which that will be a nice $1,900. We can also run a spacer under the cylinder as well a .080" spacer should lower it by about 1.5-2 points I believe but wed probably need adjustable cam gears.

How about this idea..... Ninja 300 rods? They are about 2.8mm shorter, I did some rough calculations and I think it might drop the compression to much, like down to 7-7.5:1... so if we ran the 300 rods with 12.5-13.0:1 pistons it might bring it up to the 8.5-9.0:1 ratio we'd be looking for without having to run block spacers and such?

Benefits - Newer (possibly stronger) rods, little thicker on the small end and youd get a forged piston with it.

Sorry all you N/A guys I'm trying to think of ideas for the turbo setup :-p

This thread prompted me to pretty-up a spreadsheet I put together when I put up this thread https://www.ninjette.org/forums/show...ht=compression. If anyone is interested I'll attach the live spreadsheet

Looks like (and this is assuming the new gen bore/stroke/CR is the same as the pregen) you need about 60 thousandths (1.5 mm) to get to a 9:1 CR. So about half what the 300 rods would get you. So if you can put your hands on a 0.060" gasket to run under the cylinder you'll be there.

Although like Racerx points out, we have no idea whether it will start, etc at a 9:1 CR. What do the turbo 'Busa guys run for CR?

I'm wanting to go the other way, by shaving .0125" off the block it will put the CR right at 13.5:1.

[garth285]

Yeah I cant justify the cost of Carrillo's with these engines being so cheap ya know.

As of now I'm going to stay with stock compression and head studs and E85. But I was considering with the spare engine doing a lower compression and more boost.

I might pick up some 300 engine parts for cheap and measure everything out and see what combinations I could use.

The 300 has 10.6:1 compression so those pistons might drop it to much with the piston dome and the pin relocation

[garth285]

@kxpower? the 08-12 250's have 11.6:1 compression just as an FYI

Also can you modify that sheet you posted or no?

[kxpower?]

Yeah sure can. Same bore and stroke?

[kxpower?]

Crap laptop battery is dead it'll have to wait till after trick or treating.

[garth285]

yup, how did you figure that CC Volume?

[garth285]

Originally Posted by kxpower?

Crap laptop battery is dead it'll have to wait till after trick or treating.

No rush, same here!!! lol

[kxpower?]

Originally Posted by garth285

yup, how did you figure that CC Volume?

(Displacement + CCV)/CCV = CR, I don't remember how but you just solve for CCV.

[garth285]

OK I got ya, so that should 15.55cc's should be the piston volume and combustion chamber volume.... hmmm very interesting!

[Racer x]

Originally Posted by garth285

Yeah I cant justify the cost of Carrillo's with these engines being so cheap ya know.

As of now I'm going to stay with stock compression and head studs and E85. But I was considering with the spare engine doing a lower compression and more boost.

I might pick up some 300 engine parts for cheap and measure everything out and see what combinations I could use.

The 300 has 10.6:1 compression so those pistons might drop it to much with the piston dome and the pin relocation

The rods are not that much stock compresson is good but not stock Pistons.

[Racer x]

This is some photos of the gaskets. The copper one is .040 abot four times the thickness of stock.

[Racer x]

More pictures

[micoulisninja]

Originally Posted by garth285

How about this idea..... Ninja 300 rods? They are about 2.8mm shorter, I did some rough calculations and I think it might drop the compression to much, like down to 7-7.5:1... so if we ran the 300 rods with 12.5-13.0:1 pistons it might bring it up to the 8.5-9.0:1 ratio we'd be looking for without having to run block spacers and such?

Benefits - Newer (possibly stronger) rods, little thicker on the small end and youd get a forged piston with it.

Sorry all you N/A guys I'm trying to think of ideas for the turbo setup :-p

2,9mm to be exact...
the 300 rods are indeed stronger and beefier at top end...using a couple of forged on top of them would be ideal...
I had told you that when you first presented your idea but you had rejected it as being expensive for your project...
the cheap version would be to keep stock rods and get a 300 aluminum block and pistons....the serious drawback is that the pistons are cast but on the other hand you have much lighter pistons and pins (about 10 grams less reciprocating weight on each cylinder), flat crown and better heat dissipation....

don't make it too powerful Shawn !! I am jealous already....

PS: it is really easy to make stock cam sprockets adjustable...

[garth285]

Originally Posted by micoulisninja

2,9mm to be exact...
the 300 rods are indeed stronger and beefier at top end...using a couple of forged on top of them would be ideal...
I had told you that when you first presented your idea but you had rejected it as being expensive for your project...
the cheap version would be to keep stock rods and get a 300 aluminum block and pistons....the serious drawback is that the pistons are cast but on the other hand you have much lighter pistons and pins (about 10 grams less reciprocating weight on each cylinder), flat crown and better heat dissipation....

don't make it too powerful Shawn !! I am jealous already....

PS: it is really easy to make stock cam sprockets adjustable...

I must have missed that!

What I was trying to see is if I Could use just one part for the project like the rods or the pistons, sort of a drop in and go kinda deal, the rods would have been the best... maybe I Should start looking at other bikes rod dimensions to find out what would work.

[Racer x]

Forged Pistons are pretty important. J had no trouble smashing holes in forged Pistons and compressing ring lands. I would hate to see what would happen with cast Pistons.

The stock rods are good to 120 hp according to some people I have talked to.

[garth285]

Originally Posted by Racer x

Forged Pistons are pretty important. J had no trouble smashing holes in forged Pistons and compressing ring lands. I would hate to see what would happen with cast Pistons.

The stock rods are good to 120 hp according to some people I have talked to.

Was that on nitrous?

[Racer x]

With my old system. The new syst does not do damage like that

[ninja250r81]

7:1 - 96psi
8:1 - 117psi
9:1 - 139psi
10:1 - 161psi
11:1 - 184psi
12:1 - 208psi

You allow 60% ve at cranking speed

[micoulisninja]

Originally Posted by garth285

I must have missed that!

What I was trying to see is if I Could use just one part for the project like the rods or the pistons, sort of a drop in and go kinda deal, the rods would have been the best... maybe I Should start looking at other bikes rod dimensions to find out what would work.

try the ZX-6R rods years '98-'04....
the '00 gen definetely is compatible in terms of top end since the piston pin is the exact same as for the 250 !!
I' d appreciate some feedback on your findings since I might end up doing sth like that myself...don't forget to weigh them too !!

[DaBlue1]

Has anyone looked at reducing the flywheel weight for a slight HP gain?

http://www.xlitemoto.com/products_de...b3a9dd432.html

[kxpower?]

Originally Posted by garth285

@kxpower? the 08-12 250's have 11.6:1 compression just as an FYI

Also can you modify that sheet you posted or no?

Here is the actual spreadsheet so others can fool around with it. I put in 11.6 for the stock CR and did a goal-seek to set the new CR at 9:1. As you can see you need to add about 0.050".

So go from 0.010" head gasket to 0.040" copper, and a 0.020" (maybe get copper made too?) cylinder block to crankcase seal and you're there.

[garth285]

Thank you sir! Yeah I think I need to scrap this 300 rod idea, if they were maybe only 1mm shorter it would work but yeah to much.

I'm gunna stick to stock stuff for now!
@Racer x I dont doubt nitrous did that to those pistons! Nitrous is a lot harder on pistons than boost.